Laser device and method of manufacturing the same

Abstract

A phase shift region is formed in a waveguide layer constituting a laser device. The phase shift region is a recess portion formed in the waveguide layer, and a periodic projection structure is formed on the surface of the waveguide layer including the recess portion. The recess portion can be formed by etching using an agent having weak etching anisotropy. Optical feedback can be performed while concentration of light in the phase shift region is suppressed.

I claim: 
     
       1. A laser device comprising: a substrate;   an active layer formed on the substrate;   a waveguide layer formed on the active layer and having a phase shift region, the phase shift region being a projecting portion formed in a center of the waveguide layer, a diffraction grating being formed in the entire surface of the waveguide layer including the projecting portion;   a cladding layer formed on the waveguide layer; and   electrodes formed on the cladding layer.   
     
     
       2. A laser device comprising: a substrate;   an active layer formed on the substrate;   a waveguide layer formed on the active layer and having a phase shift region, the phase shift region being a recessed portion formed in a center of the waveguide layer, a diffraction grating being formed in the entire surface of the waveguide layer including the recessed portion, the diffraction grating defining a pattern in the entire surface of the waveguide layer, wherein the diffraction grating pattern in the recessed portion is less pronounced than the diffraction grating pattern in other portions of the waveguide layer;   a cladding layer formed on the waveguide layer; and   electrodes formed on the cladding layer.   
     
     
       3. A method for manufacturing a laser device, comprising the steps of: forming an active layer on a substrate;   forming a waveguide layer on the active layer;   forming a diffraction grating in an entire surface of the waveguide layer by use of a two-beam interference exposure method employing a laser, the diffraction grating defining a pattern in the entire surface of the waveguide layer;   forming a mask on a portion of the diffraction layer of the waveguide layer;   etching the waveguide layer by use of an etchant having weak etching anisotropy to form a recessed portion, the diffraction grating pattern in the recessed portion being less pronounced than the diffraction grating pattern in other portions of the waveguide layer;   forming a cladding layer on the waveguide layer by removing the mask; and   forming electrodes on the cladding layer.   
     
     
       4. The laser device according to claim 3, wherein the etching step includes partially thinning a portion of the waveguide layer to form the recessed portion in the waveguide layer, the recessed portion serving as a phase shift region. 
     
     
       5. The laser device according to claim 3, wherein the etchant having weak etching anisotropy comprises a sulfuric acid. 
     
     
       6. A method for manufacturing a laser device, comprising the steps of: forming an active layer on a substrate;   forming a waveguide layer on the active layer;   forming a diffraction grating in an entire surface of the waveguide layer by use of a two-beam interference exposure method employing a laser, the diffraction grating defining a pattern in the entire surface of the waveguide layer;   forming a mask on a portion of the diffraction grating of the waveguide layer;   etching the waveguide layer by use of an etchant having strong etching anisotropy, the etchant substantially maintaining the pattern defined by the diffraction grating in the entire surface of the waveguide layer;   forming a cladding layer on the waveguide layer by removing the mask; and   forming electrodes on the cladding layer.   
     
     
       7. The laser device according to claim 6, wherein the etching step includes etching the waveguide layer to form a projecting portion serving as a phase shift region, the diffraction grating pattern in the projecting portion being substantially the same as the diffraction grating pattern in other portions of the waveguide layer. 
     
     
       8. The laser device according to claim 7, wherein the etchant having strong etching anisotropy comprises a hydrogen bromide.